A team has developed a nonlinear camera capable of capturing high-resolution images of the interior of solid objects using terahertz (THz) electromagnetic waves. Images produced using THz radiation are called hyperspectral because the image consists of pixels, each containing the electromagnetic signature of the object in that point.
Lying between microwaves and infrared in the electromagnetic spectrum, THz radiation easily penetrates materials like paper, clothes, and plastic in the same way X-rays do but without being harmful. It is safe to use with even the most delicate biological samples. THz imaging makes it possible to see the molecular composition of objects and distinguish between different materials such as sugar and cocaine, for example.
The fingerprint of all the details of the image is preserved in such a way that the nature of the object can be investigated in full detail. Until now, cameras capable of capturing a hyperspectral image preserving fine details revealed by THz radiation had not been considered possible.
The team used a single-pixel camera to image sample objects with patterns of THz light. The prototype can detect how the object alters different patterns of THz light. By combining this information with the shape of each original pattern, the camera reveals the image of an object as well as its chemical composition.
Sources of THz radiation are very faint and hyperspectral imaging had, until now, limited fidelity. To overcome this, the team shone a standard laser onto a unique nonlinear material capable of converting visible light to THz. The prototype camera creates THz electromagnetic waves very close to the sample, similar to how a microscope works. As THz waves can travel right through an object without affecting it, the resulting images reveal the shape and composition of objects in three dimensions.
The next phase of research will be in speeding up the image reconstruction process and applying THz cameras to real-world applications such as airport security, intelligent car sensors, quality control in manufacturing, and scanners to detect health problems like skin cancer.
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